TAPS Working Group P. Tiesel
Internet-Draft T. Enghardt
Intended status: Experimental A. Feldmann
Expires: April 30, 2018 TU Berlin
October 27, 2017
Socket Intents
draft-tiesel-taps-socketintents-01
Abstract
This document outlines Socket Intents, a concept that allows
applications to share their knowledge about upcoming communication
and express their performance preferences in a generic, intuitive
and, portable way. Using Socket Intents, an application can express
what it knows, assumes, expects, or wants regarding its network
communication. The information provided by Socket Intents can be
used by the network stack to optimize communication in a best-effort
way.
Socket Intent can be used to stem against the complexity of
exploiting transport diversity, e.g., to automate the choice among
multiple paths, provisioning domains or protocols. By shifting this
complexity from the application developer to the operating system, it
enables the use of these transport features to a wider range of
applications.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
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Internet-Drafts are draft documents valid for a maximum of six months
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This Internet-Draft will expire on April 30, 2018.
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Copyright Notice
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Table of Contents
1. Conventions and Definitions . . . . . . . . . . . . . . . . . 3
2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Problem Statement . . . . . . . . . . . . . . . . . . . . . . 3
4. Socket Intents Concept . . . . . . . . . . . . . . . . . . . 4
4.1. Interactions between Socket Intents and QoS . . . . . . . 5
5. Socket Intent Types . . . . . . . . . . . . . . . . . . . . . 5
6. Initial Socket Intent Types . . . . . . . . . . . . . . . . . 6
6.1. Traffic Category . . . . . . . . . . . . . . . . . . . . 6
6.2. Size to be Sent / Received . . . . . . . . . . . . . . . 7
6.3. Duration . . . . . . . . . . . . . . . . . . . . . . . . 7
6.4. Stream Bitrate Sent / Received . . . . . . . . . . . . . 7
6.5. Burstiness . . . . . . . . . . . . . . . . . . . . . . . 7
6.6. Timeliness . . . . . . . . . . . . . . . . . . . . . . . 8
6.7. Disruption Resilience . . . . . . . . . . . . . . . . . . 9
6.8. Cost Preferences . . . . . . . . . . . . . . . . . . . . 9
7. Implementation Guidelines . . . . . . . . . . . . . . . . . . 10
8. Security Considerations . . . . . . . . . . . . . . . . . . . 10
8.1. Performance Degradation Attacks . . . . . . . . . . . . . 10
8.2. Information Leakage . . . . . . . . . . . . . . . . . . . 11
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11
10. Publications History . . . . . . . . . . . . . . . . . . . . 11
11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 11
12. References . . . . . . . . . . . . . . . . . . . . . . . . . 11
12.1. Normative References . . . . . . . . . . . . . . . . . . 11
12.2. Informative References . . . . . . . . . . . . . . . . . 12
Appendix A. Usage examples . . . . . . . . . . . . . . . . . . . 13
A.1. Example 1 . . . . . . . . . . . . . . . . . . . . . . . . 13
A.2. Example 2 . . . . . . . . . . . . . . . . . . . . . . . . 13
A.3. Example 3 . . . . . . . . . . . . . . . . . . . . . . . . 14
Appendix B. Changes . . . . . . . . . . . . . . . . . . . . . . 14
B.1. Since -00 . . . . . . . . . . . . . . . . . . . . . . . . 14
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Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 15
1. Conventions and Definitions
The words "MUST", "MUST NOT", "SHALL", "SHALL NOT", "SHOULD", and
"MAY" are used in this document. It's not shouting; when these words
are capitalized, they have a special meaning as defined in [RFC2119].
Association Set, Association, Stream, or Message are used as defined
in [I-D.tiesel-taps-communitgrany].
2. Introduction
Despite recent advances in the transport area, the adaption of new
transport protocols and transport protocol features is slow. In
practice, this only happens in limited fields as Web browsers or
within datacenters. The same problem occurs for taking advantage of
paths or provisioning domains (PvDs). In both cases, the benefits of
the new transport diversity come at the cost of an increased
complexity that has to be mastered by the application programmer.
To enable transport features like TCP fast open [RFC7413] or to
control how MPTCP [RFC6824] creates subflows requires specialized
APIs. These APIs are not part of the standard socket API, usually
not portable, and not available in many programming languages. Using
them often requires profound knowledge of the transport protocol
internals.
To use multiple paths, applications usually have to use their own
heuristics to select which paths, provisioning domains, or access
network to use. Choosing the right path is difficult as their
characteristics differ, e.g., regarding performance. Obtaining the
necessary information is difficult since it may require special
privileges and non-portable APIs.
In all cases mentioned above, an application that wants to take
advantage of the available transport diversity is faced with
substantially higher complexity regarding network APIs and networking
code.
3. Problem Statement
Application programmers opening a communication channel typically
know how this channel will be used. There is more information
available than the protocol and destination address needed to
establish a communication channel: An application developer has an
intuition about many aspects of an upcoming communication. These
intuition may include:
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preferences: whether to optimize for bandwidth, latency, or cost
characteristics: expected packet rates, byte rates or how many bytes
will be sent or received.
expectations: towards path availability or packet loss
resiliences: whether the application can gracefully handle certain
error cases
These preferences, expectations and other information known about the
upcoming communication should be expressible in an intuitive, generic
way, that is independent of the network and transport protocol. Its
representation should be independent of the actual API used for
network communication and should be expressible in whatever API
available, e.g., as socket options for BSD sockets or as part of the
address resolution configuration for Post Sockets
[I-D.trammell-taps-post-sockets].
Socket Intents should enable the OS to adjust the communication
channel according to the application's intents in a best-effort
fashion: They should provide the information needed to automatically
enabling transport features the application can benefit from or help
choosing the most suitable (combination) of paths based on the
properties of the access networks or PvD (see [RFC7556], Section 6.2)
available. The actual implementation is not part of the Socket
Intents concept, it is left to an OS policy that may choose the best
transport protocol, default parameters and PvDs available and may
also try to further optimize wherever possible.
4. Socket Intents Concept
Socket Intents are pieces of information that allow an application to
express what they know about the application's communication. They
indicate what the application wants to achieve, knows, or assumes in
general, intuitive terms. An application can use them to annotate
the characteristics, preferences, and intentions it associates with
each communication unit. Depending on the API used, Socket Intents
can be used on a per Association Set, Association, Stream or, Message
level.
Socket Intents are optional information that can be considered in a
_best-effort_ manner. Socket Intents _do not include requirements_,
such as reliable in-order delivery. Typical examples include desired
transport characteristics, e.g., low delay, high throughput, or
minimal cost, as well as expected application behavior, e.g., will
send 500 bytes. As this information captures the intents of an
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applications and passes them along with the communication socket, we
call these pieces of information Socket Intents.
Applications have an incentive to specify their intents as accurately
as possible to take advantage of the most suitable existing
resources. Applications are expected to selfishly specify their
preferences. It is up to the OS's policy to prevent commitment of
excessive resources.
4.1. Interactions between Socket Intents and QoS
Socket Intents are not QoS labels, but have an orthogonal meaning.
While the purpose of QoS is to specify what an application requires,
Socket Intents are used to specify what an application knows or
prefers. Therefore,
o Socket Intents SHALL be purely advisory.
o Socket Intents MUST NOT be used to derive IntServ / RSVP style
guarantees.
o Socket Intents SHOULD be taken into account on a best-effort basis
and MAY be used to derive DiffServ Service Classes as described in
[RFC4594].
5. Socket Intent Types
Socket Intents are structured as key-value-pairs.
The key, called short name, specifies the Socket Intent type. It is
identified by a string of the lower-case characters [a-z], numbers
[0-9] and the separator "-".
The namespace for the short names is partitioned as follows:
o All Socket Intent type not starting with "x-" or "y-" are managed
by an IANA registry. The assignment of new types requires an RFC
or expert review (TO BE DECIDED).
o Socket Intent type starting with "x-" are for experimental use.
o Private or vendor specific Socket Intent type MUST start with
"y-[vendor]-".
Values can be represented as Enum, Int, Float, ASCII-String [RFC0020]
or a sequence of the aforementioned data types. Implementations
determine how these types are represented on the respective platform.
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The data type for the individual Socket Intents are determined by the
document defining the Socket Intent and MUST NOT be changed by an
implementation. For Enum data types, a list of valid values MUST be
provided by the document specifying that intent as well as a default
value that is equivalent to not specifying this intent.
6. Initial Socket Intent Types
The following sections contain a list or Socket Intent types and
their possible values. Recommended default values for Enum values
are marked with an asterisk (*) behind the level name.
6.1. Traffic Category
The Traffic Category describes the dominating traffic pattern of the
respective communication unit expected by the application.
Short name: category
Applicability: Association Set, Association, Stream
Data type: Enum
+---------+---------------------------------------------------------+
| Level | Description |
+---------+---------------------------------------------------------+
| query | Single request / response style workload, latency bound |
| | |
| control | Long lasting low bandwidth control channel, not |
| | bandwidth bound |
| | |
| stream | Stream of bytes/messages with steady data rate |
| | |
| bulk | Bulk transfer of large messages, presumably bandwidth |
| | bound |
| | |
| mixed* | Don't know or none of the above |
+---------+---------------------------------------------------------+
Note: Most categories suggest the use of other intents to further
describe the traffic pattern anticipated, e.g., the bulk category
suggesting the use of the Size to be Sent intent or the stream
category suggesting the Stream Bitrate and Duration intents.
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6.2. Size to be Sent / Received
This Intent is used to communicate the expected size of a transfer.
Short name: send_size / recv_size
Applicability: Association Set, Association, Stream, Message
Data type: Int (bytes)
6.3. Duration
This Intent is used to communicate the expected lifetime of the
respective communication unit.
Short name: duration
Applicability: Association Set, Association, Stream
Data type: Int (msec)
6.4. Stream Bitrate Sent / Received
This Intent is used to communicate the bitrate of the respective
communication unit.
Short name: send_bitrate / recv_bitrate
Applicability: Association Set, Association, Stream
Data type: Int (bits/sec)
6.5. Burstiness
This Intent describes the anticipated burst characteristics of the
traffic for this communication unit. It expresses how the traffic
sent by the application is expected to vary over time, and,
consequently, how long sequences of consecutively sent packets will
be. Note that the actual burst characteristics of the traffic at the
receiver side will depend on the network.
This Intent can provide hints to the application on what the resource
usage pattern for this communication unit will look like, which can
be useful for balancing the requirements of different application.
Short name: bursts
Applicability: Association Set, Association, Stream
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Data type: Enum
+----------------+--------------------------------------------------+
| Level | Description |
+----------------+--------------------------------------------------+
| no_bursts | Application sends traffic at a constant rate |
| | |
| regular_bursts | Application sends bursts of traffic periodically |
| | |
| random_bursts | Application sends bursts of traffic irregularly |
| | |
| bulk | Application sends a bulk of traffic |
| | |
| mixed* | Don't know or none of the above |
+----------------+--------------------------------------------------+
6.6. Timeliness
This Intent describes the desired delay characteristics for this
communication unit. It provides hints for the OS whether to optimize
for low delay or for other criteria. There are no hard requirements
or implied guarantees on whether these requirements can actually be
satisfied.
Short name: timeliness
Applicability: Association Set, Association, Stream, Message
Data type: Enum
+-------------+-----------------------------------------------------+
| Level | Description |
+-------------+-----------------------------------------------------+
| stream | Delay and packet delay variation should be kept as |
| | low as possible |
| | |
| interactive | Delay should be kept as low as possible, but some |
| | variation is tolerable |
| | |
| transfer* | Delay and packet delay variation should be |
| | reasonable, but are not critical |
| | |
| background | Delay and packet delay variation is no concern |
+-------------+-----------------------------------------------------+
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6.7. Disruption Resilience
This Intent describes how an application deals with disruption of its
communication, e.g. connection loss. It communicates how well the
application can recover from such disturbance and can have
implications on how many resources the OS should allocate to failover
techniques for this particular communication unit.
Short name: resilience
Applicability: Association Set, Association, Stream, Message
Data type: Enum
+--------------+----------------------------------------------------+
| Level | Description |
+--------------+----------------------------------------------------+
| sensitive | Disruptions result in application failure, |
| | disrupting user experience |
| | |
| recoverable* | Disruptions are inconvenient for the application, |
| | but can be recovered from |
| | |
| resilient | Disruptions have minimal impact for the |
| | application |
+--------------+----------------------------------------------------+
6.8. Cost Preferences
This describes the Intents of an Application towards costs cased by
the respective communication unit. It should guide the OS how to
handle cost vs. performance and reliability tradeoffs.
Short name: cost
Applicability: Association Set, Association, Stream, Message
Data type: Enum
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+---------------+---------------------------------------------------+
| Level | Description |
+---------------+---------------------------------------------------+
| no_expense | Avoid expensive transports and consider failing |
| | otherwise |
| | |
| optimize_cost | Prefer inexpensive transports and accept service |
| | degradation |
| | |
| balance_cost* | Do not bias balancing cost and other criteria |
| | |
| ignore_cost | Ignore cost, choose transport solely based on |
| | other criteria |
+---------------+---------------------------------------------------+
Note: the "no_expense" level implicitly asks the OS to fail
communication attempts if no inexpensive transports are available.
Application developers MUST be aware that this also no hard
requirement and can be ignored or overridden by the OS policy.
7. Implementation Guidelines
Implementations faced with unknown Socket Intent types SHOULD ignore
these intents for forward compatibility. The API MAY include a
parameter to change this behavior and make specifying unknown Socket
Intent types return an error.
Invalid values SHOULD return an error to the application.
For debugging purposes, implementations SHOULD allow to enumerate the
Socket Intents that are understood by the implementation. They MAY
expose which of the Socket Intents were considered by the
implementation.
8. Security Considerations
8.1. Performance Degradation Attacks
We assume that applications specify their preferences in a selfish,
but not malicious way and that it is up to the OS to find a
compromise between demands.
A malicious application could confuse the OS in a way that leads to
scheduling traffic with certain Intents on a more expensive
interface, penalizing this traffic, or even rejecting it. The attack
vector added by this is negligible: As the malicious application
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could also generate the traffic it claims to intend, it already has a
much more powerful attack vector.
As a mitigation, the OS could monitor and compare the intents
specified with the traffic actually generated and notify the user if
the usage of Socket Intents is unusual or defective.
8.2. Information Leakage
Varying the transport or IP layer parameters of packets belonging to
different Streams or Messages multiplexed in the same encrypted
association might enable an attacker to gain some ground truth about
the shares of different kinds of traffic. As this might also be
implied by packet timings, application developers might weight the
small additional information disclosure against the possible
performance gains. Using Socket Intents on Association level can be
considered safe.
9. IANA Considerations
The Socket Intents type namespace SHOULD be managed by the IANA
registry. Details conforming to [RFC5226] are laid out in Section 5,
the initial types for the registry are described in Section 6.
10. Publications History
o The original idea of Socket Intents was published in [CoNEXT2013].
o A performance study "Socket Intents: OS Support for Using Multiple
Access Networks and its Benefits for Web Browsing" is under
submission.
11. Acknowledgements
This work has been supported by Leibniz Prize project funds of DFG -
German Research Foundation: Gottfried Wilhelm Leibniz-Preis 2011 (FKZ
FE 570/4-1).
12. References
12.1. Normative References
[RFC0020] Cerf, V., "ASCII format for network interchange", STD 80,
RFC 20, DOI 10.17487/RFC0020, October 1969,
<https://www.rfc-editor.org/info/rfc20>.
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[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", RFC 5226,
DOI 10.17487/RFC5226, May 2008,
<https://www.rfc-editor.org/info/rfc5226>.
12.2. Informative References
[CoNEXT2013]
Schmidt, P., Enghardt, T., Khalili, R., and A. Feldmann,
"Socket intents", Proceedings of the ninth ACM conference
on Emerging networking experiments and technologies -
CoNEXT '13, DOI 10.1145/2535372.2535405, 2013.
[DASH] International Organization for Standardization, "Dynamic
adaptive streaming over HTTP (DASH) - Part 1: Media
presentation description and segment formats", Standard
ISO/IEC 23009-1:2014 , June 2011,
<https://www.iso.org/standard/65274.html>.
[I-D.pauly-taps-guidelines]
Pauly, T., "Guidelines for Racing During Connection
Establishment", draft-pauly-taps-guidelines-01 (work in
progress), October 2017.
[I-D.tiesel-taps-communitgrany]
Tiesel, P. and T. Enghardt, "Communication Units
Granularity Considerations for Multi-Path Aware Transport
Selection", draft-tiesel-taps-communitgrany-01 (work in
progress), October 2017.
[I-D.trammell-taps-post-sockets]
Trammell, B., Perkins, C., Pauly, T., Kuehlewind, M., and
C. Wood, "Post Sockets, An Abstract Programming Interface
for the Transport Layer", draft-trammell-taps-post-
sockets-03 (work in progress), October 2017.
[RFC4594] Babiarz, J., Chan, K., and F. Baker, "Configuration
Guidelines for DiffServ Service Classes", RFC 4594,
DOI 10.17487/RFC4594, August 2006,
<https://www.rfc-editor.org/info/rfc4594>.
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[RFC4960] Stewart, R., Ed., "Stream Control Transmission Protocol",
RFC 4960, DOI 10.17487/RFC4960, September 2007,
<https://www.rfc-editor.org/info/rfc4960>.
[RFC6824] Ford, A., Raiciu, C., Handley, M., and O. Bonaventure,
"TCP Extensions for Multipath Operation with Multiple
Addresses", RFC 6824, DOI 10.17487/RFC6824, January 2013,
<https://www.rfc-editor.org/info/rfc6824>.
[RFC7413] Cheng, Y., Chu, J., Radhakrishnan, S., and A. Jain, "TCP
Fast Open", RFC 7413, DOI 10.17487/RFC7413, December 2014,
<https://www.rfc-editor.org/info/rfc7413>.
[RFC7556] Anipko, D., Ed., "Multiple Provisioning Domain
Architecture", RFC 7556, DOI 10.17487/RFC7556, June 2015,
<https://www.rfc-editor.org/info/rfc7556>.
Appendix A. Usage examples
A.1. Example 1
Consider a cellphone performing an OS upgrade. This process usually
implies downloading a large file. This is a bulk transfer for which
the application may already know the file size. Timing is typically
noncritical and the data can be downloaded as background traffic with
minimal cost and power overhead. It would not hurt if the TCP
connection was closed during the transfer as the download can be
continued.
For this case, the application should set the "Traffic Category" to
"bulk", "Timeliness" to "background", and "Application Resilience" to
"resilient". In addition, "Message Size to be Received" can be
provided. Finally, the application may set the the "Cost
Preferences" to "no_expense".
The OS can use this information and therefore may schedule this
transfer on a flaky but not traffic-billed WiFi link and may reject
the connection attempt if no cheap access link is available.
A.2. Example 2
Consider a user watching non-live video content using MPEG-DASH
[DASH]. This usually means fetching a stream of video chunks. The
application should know the size of each chunk and may know the
bitrate and the duration of each chunk and the whole video.
Disconnection of the TCP connection should be avoided because that
might have an effect that is visible to the user.
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For this case, the application should set the "Traffic Category" to
"stream", the "Timeliness" to "stream", and "Application Resilience"
to "sensitive". It may also provide the "Stream Bitrate Received"
and "Duration" expected. Finally, the application may set the the
"Cost Preferences" to "balance_cost".
The OS can use this information and, e.g, use MPTCP [RFC6824] if
available to schedule the traffic on the cheaper link (e.g, WiFi)
while establishing an additional subflow over an expensive link
(e.g., LTE). If the desired bandwidth cannot be matched by the
cheaper link, the more expensive link can be added to satisfy the
desired bandwidth.
If the application would set the "Cost Preferences" to
"optimize_cost", the OS would not schedule traffic on the second
subflow and the application would reduce the video quality to adapt
to the available data rate.
A.3. Example 3
Consider a user managing a remote machine via SSH. This usually
involves at least one long-lived console session and possibly file
transfers using SCP or rsync multiplexed on the same association
(e.g. TCP connection).
For the packets sent for the console session, the application can set
the "Traffic Category" to "control", the "Burstiness" to "random
bursts", the timeliness to "interactive" and the resilience to
"sensitive". For the packets of the file transfers, SSH may set
both, the "Traffic Category" and "Burstiness" to "bulk". It may also
know the size of the transfer and therefore sets "Message Size to be
Sent" or "Message Size to be Received".
Assuming there are transport opportunities supporting multiple
streams in a single association (e.g. SCPT [RFC4960]), the OS can
use this information to schedule the streams over different links to
meet their requirements (latency vs. bandwidth). In case the OS has
to use TCP, it can still optimize by disabling TCP Nagle Algorithm
for console session related transmissions.
Appendix B. Changes
B.1. Since -00
o Updates on Terminology (Object -> Message, Flow -> Assocication)
o More detailed Socket Intent Types specification
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o Added implementation guidelines
o Many clairfications
o Fixed Authors and affiliations
Authors' Addresses
Philipp S. Tiesel
TU Berlin
Marchstr. 23
Berlin
Germany
Email: philipp@inet.tu-berlin.de
Theresa Enghardt
TU Berlin
Marchstr. 23
Berlin
Germany
Email: theresa@inet.tu-berlin.de
Anja Feldmann
TU Berlin
Marchstr. 23
Berlin
Germany
Email: anja@inet.tu-berlin.de
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